1. Field of the Invention
The present invention relates to magnetic sensing elements utilizing the tunneling effect and incorporated in, for example, hard disk drives and other magnetic sensing devices. In particular, the present invention relates to a tunneling magnetic sensing element having low variations in RA and the rate of resistance change (ΔR/R) and having a low interlayer coupling magnetic field Hin.
2. Description of the Related Art
Tunneling magnetic sensing elements (tunneling magnetoresistive (TMR) elements) change their resistance utilizing the tunneling effect. When the magnetization direction of a pinned magnetic layer is antiparallel to that of a free magnetic layer, a tunneling current does not easily flow through an insulating barrier layer (tunnel barrier layer) between the pinned magnetic layer and the free magnetic layer; hence, the resistance is maximized. On the other hand, when the magnetization direction of the pinned magnetic layer is parallel to that of the free magnetic layer, the tunneling current most easily flows; hence, the resistance is minimized.
A change in electrical resistance due to a change in the magnetization of the free magnetic layer affected by an external magnetic field is detected as a change in voltage on the basis of this principle to detect a leakage field from a recording medium.
Japanese Unexamined Patent Application Publication Nos. 2005-286340 (Patent Document 1) and 2005-260226 (Patent Document 2) are examples of related art.
The interlayer coupling magnetic field Hin acts between the free magnetic layer and the pinned magnetic layer. An increase in interlayer coupling magnetic field Hin results in a decrease in the magnetic sensitivity of the free magnetic layer and an increase in the asymmetry of a waveform when the element functions as a magnetic head. Thus, the element is designed so as to reduce the interlayer coupling magnetic field Hin.
For example, when a metal layer constituting the insulating barrier layer is subjected to oxidation treatment, the promotion of oxidation can reduce the interlayer coupling magnetic field Hin.
However, the employment of the technique disadvantageously increases RA (resistance R×element area A) of the tunneling magnetic sensing element. In this case, for example, the design value of the height of the tunneling magnetic sensing element (MRh) must be changed in order to bring RA within a predetermined range.
However, the change in the height of the element increases variations in the asymmetry of the waveform and reduces a signal-to-noise ratio. That is, the change in the height of the element cannot appropriately respond to an increase in recording density.
Accordingly, it is desirable that the interlayer coupling magnetic field Hin is reduced without redesign of the element while the variations in RA is small. In this case, it is desirable that the interlayer coupling magnetic field Hin is reduced while variations in the rate of resistance change (ΔR/R) are also small.
In Patent Document 1 described above, a first pinned layer and a second pinned layer include a Cu sublayer or a Ta sublayer. However, the reason for the disposition of the Cu sublayer and the Ta sublayer is not apparent. In any case, Patent Document 1 discloses an invention for the stable application of an exchange bias magnetic field from a longitudinal bias layer disposed on the free magnetic layer to the free magnetic layer.
Patent Document 2 does not describe the tunneling magnetic sensing element. In Patent Document 2, an upper pinned layer includes an insertion sublayer for increasing interface scattering.
In Patent Documents 1 and 2, the problems with the tunneling magnetic sensing element are not recognized. That is, no means for solving the problems is described in Patent Documents 1 and 2.